// https://leetcode-cn.com/problems/combination-sum-iii/
// 216. 组合总和 III

#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <queue>
#include <limits.h>

using namespace std;

// struct ListNode {
//     int val;
//     ListNode *next;
//     ListNode() : val(0), next(nullptr) {}
//     ListNode(int x) : val(x), next(nullptr) {}
//     ListNode(int x, ListNode *next) : val(x), next(next) {}
// };

// struct TreeNode {
//     int val;
//     TreeNode *left;
//     TreeNode *right;
//     TreeNode() : val(0), left(nullptr), right(nullptr) {}
//     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
//     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
// };



class Solution {
public:
    vector<vector<int>> combinationSum3(int k, int n) {
        backtrace(k, n, 0, 1);
        return result;
    }

private:
    vector<vector<int>> result;
    vector<int> group;

    void backtrace(int k, int n, int sum, int start_index) {
        if (group.size() > k) return;
        if (sum > n) return;

        if (group.size() == k && sum == n) {
            result.push_back(group);
            return;
        }
        
        for (int i = start_index; i <= 9; i++) {
            sum += i;
            group.push_back(i);
            backtrace(k, n, sum, i+1);
            sum -= i;
            group.pop_back();
        }

    }
};



int main() {
    Solution obj = Solution();
}